1. Field of the Invention
The present invention relates to a compact type-printer using a type ring train.
2. Description of the Related Art
Known printers that are provided with a type ring train and type selection mechanisms are described in Japanese Patent Applications Laid-Open Nos. 53-15927 and 53-49527, for example. In these printers, desired types for printing are selected by engaging and stopping rotating type rings by means of select levers.
FIG. 12 shows an outline of a type selection mechanism of the printer of this type. A select lever 60 is formed of a magnetic material, and its central part is rotatably supported by a shaft 63. The upper end part of the lever 60 is provided with an engaging portion 62 that engages a type ring 61. The select lever 60 rotates around the shaft 63 as its lower end part is driven by electromagnetic means. The electromagnetic means is composed of a magnetization coil 64 and a permanent magnet 65. The coil 64 is located so as to enclose the lower part of the select lever 60, while the magnet 65 is opposed to the lower end of the lever 60. The permanent magnet 65 has yokes 66 and 67 on its N and S poles, respectively. The lower end part of the lever 60 moves between the N- and S-side yokes 66 and 67. If the magnetization coil 64 imparts N or S polarity to the lower end of the select lever 60, attractive and repulsive forces act between the yokes 66 and 67, whereupon the select lever 60 rocks.
In FIG. 12, numeral 69 denotes a drive shaft; 70, reset cam; 71, type; 72, platen; 73, printing paper; 74, ink ribbon; and 75, character selection teeth engaging with the engaging portion 62.
The type selection mechanism constructed in this manner operates with reliability and consumes little power. The lower end part of the select lever 60 is located between the N- and S-side yokes 66 and 67. When the lever 60 is driven by the electromagnetic means, it runs against the respective side faces of the yokes 66 and 67 and is positioned. In this case, direct contact between the magnetic members considerably varies attractive force that is based on magnetic force, depending on the extent of treatment on the contact surfaces of the members. If a nonmagnetic film 68 is set between the select lever 60 and the yokes 66 and 67 in order to ease the shock of a collision, the magnetic force is weakened, so that the action of the select lever 60 is destabilized. If a trace of dust (about 0.1-mm particles) is trapped between the lever 60 and the yokes 66 and 67, moreover, the contact between these members is rendered unstable, and abrasion of contact regions must be taken into consideration.